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Old August 30, 2012, 08:19 AM   #26
Bart B.
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Once I used an optical comparitor at work to sort 200 Sierra .308 190-gr. HPMK's by ogive shape. Ended up with four sets of bullets. Then weighed each set and sorted them into 2/10ths grain spreads; four groups of these sub groups. And finally measured all for length; 3 sets of these in each sub-sub-group. Yikes; what a mess to organize!!!!!

Fired each few-bullet group on a test target at 600 yards from full length sized cases whose case headspace had a 2/1000ths spread (head to shoulder datum). All groups were about 3.5 inches as I held the scoped rifle on bags slung up in prone. Then fired three 10-shot groups with 30 unsorted bullets from the same lot. They too, produced groups about 3.5 inches.

Wasted my time sorting bullets. Never did it again. I'm convinced there's more inaccuracy caused by bullet unbalance than what length and weight measurements can statically be made. You gotta spin bullets at least 30 to 40 thousand rpm to test their balance. No tools do that I know of.

I once did a test with a dozen or so different seating dies. Standard ones in a set you buy, Vickerman, Wilson chamber type, Bonanza floating chamber, RCBS competition and others many folks swear by. Cases used had been marked on their neck with the high point and amount of neck runtout relative the case axis. After seating a couple hundred bullets, they all aligned themselves with the case neck and ended up with runout high point and amount well aligned with the case neck.

Redding's web site has an article about bullet seating. Boils down to if you case neck ain't straight on the case, nothing's gonna seat a bullet in that case with zero runout. Some seaters may reduce it a bit, but the best thing to do is end up with a straight case neck in the sizing process. Full length sizing dies with bushings make the straightest case necks and best centered ones on case shoulders. These dies have necks very well aligned with the body section just like chambers in barrels properly reamed. Such dies hold the case body solidly in place while the fired case neck's being sized down only as much as needed to hold the bullet and keeps both body and neck axis in line. No wonder the benchresters have been going away from neck sizing and doing more full length sizing.

Last edited by Bart B.; August 30, 2012 at 08:37 AM.
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Old August 31, 2012, 11:39 PM   #27
miykael
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Ogives & Barnes LRX Testing

I'm in the learning process of handloading too, and finally (2 yrs later) bought a Hornady OAL gauge & bullet comparator. I don't compete yet but I figure that the best knowledge on making consistent ammo will be found with the benchrest community.

My hunting (target was 175 SMK) setup:
Rifle - Savage 10 Precision Carbine in .308
Lapua Brass
CCI Primers
Barnes LRX 175g Bullets
IMR XBR 8208 powder

So, I spent a while not only measuring weight but also bullet ogive (after checking my rifle's chamber).

With my novice measuring results on the LRX bullets, I got this many at these Ogive measurements (the box had 51 bullets):

.806 - 3
.807 - 7
.808 - 8
.809 - 7
.810 - 14
.811 - 6
.812 - 3
.813 - 2
.815 - 1

Yes, I measured weights too, which 80% was 175-175.36gn (no including my error, scale error). Using a digital scale that weighs to 2/100ths gn.

My rifle measured 2.244" and with Barnes recommending Jump 0.050, will load OAL at ogive to 2.194. Of course later I will keep changing up/down but this was my start point.

I will keep modifying until I can wring out the best group from this bullet/rifle combo I love copper now and won't go back to lead (even if I'm sacrificing a little accuracy/speed) - except for target shooting.

If you're goal is accurizing for hunting, work your way to a bullet that works for you (I started with Nosler BT's which were great but the Barnes are better).
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Old September 1, 2012, 05:53 AM   #28
Bart B.
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Quote:
I figure that the best knowledge on making consistent ammo will be found with the benchrest community.
There's another shooting community whose rifles and ammo shoots just as accurate (sometimes better than) what the benchrest one does. And with 1/5th the case prep and no bullet weighing or measuring whatsoever. They shoot full length sized cases, too.

Quote:
Yes, I measured weights too, which 80% was 175-175.36gn (no including my error, scale error). Using a digital scale that weighs to 2/100ths gn.
How much change in a bullet's ballistic coefficient will a 1/10th grain difference in its weight make?
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Old September 1, 2012, 07:44 AM   #29
miykael
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?

1/10 gn difference...not sure...that's what I'm trying to find out I thought the benchrest crowd is the leading edge of ammo making? Just sharing and trying to learn.

Physics is physics. The real aerodynamics crowd (in aerospace and the like, that model super/hypersonic) would know the answers to weight/shape of projectiles. At 3000 fps, I'm sure any little variations on a bullet make a difference (but not much at short ranges). A dirty aeroplane surface has more drag than a clean one, so even minute changes will have some effect on a fast moving projectile...

Last edited by miykael; September 1, 2012 at 07:52 AM.
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Old September 1, 2012, 12:37 PM   #30
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One method of calculating ballistic coefficient is to divide the sectional density of the bullet by its form factor. The sectional density varies directly with weight. Your weight spread is a tiny 0.205%, so that's how much the ballistic coefficient will change due to weight. I'm not familiar with the BC's or your particular bullet, but for a 175 Sierra MatchKing fired at 2640 fps, the difference will be about 0.7" of elevation and 0.04"/mph of windage at 1000 yards.

Keep in mind that group size from error sources measured in isolation, when they are interacting in combination with one another, add together like standard deviations do: as the square root of the sum of the squares of the contribution in isolation. If you can shoot 0.5 moa at 1000 yards (the world record for a 10 shot groups at 1000 yards is 3/8 moa, IIRC, so you'd need to be a world record class shot to do this), then adding that 0.067 moa error (0.7" at 1000 yards is about 0.067 moa) will open your 0.5 moa groups to 0.504 moa on average, or about 1/22" on average at 1000 yards. It's so small because the random chance of any particular shot in the group not happening to be in the exact same direction as the weight error source would need to add directly to the group size is small.

Obviously the error contribution will be smaller at closer ranges.
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Last edited by Unclenick; September 2, 2012 at 04:14 PM. Reason: correction and clarification
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Old September 1, 2012, 04:38 PM   #31
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I have an old hexagonal Sinclair bullet comparator for seating measuring how deep from bullet was seated relative to the ogive. I don't use it anymore.

If the bottle neck rifle ammo will fit in the magazine, I seat bullets longer and longer until they start getting stuck when I extract the cartridge without firing. Then I seat the bullets halfway between touching the lands and getting stuck. I can see how long the lands scratch marks are on the bullet. I adjust the seater die to make the scratches half that long.

Old fashioned over all length measurements are good enough for my current process. With a heavy barrel, light bullet, and no wind, I would expect some groups under 1/2" at 100 yards.

I can load accurate ammo without much attention to OAL. I can also compensate for range. What is holding me back is being a putz at wind doping at 600 yards.
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Old September 2, 2012, 04:22 PM   #32
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My sort of rule of general rule of thumb is that if a gun is in perfect condition you can probably get down to around 1/2 moa without fussing with seating depth (though Berger makes a good case for their secant ogive VLD's being an exception that need fiddling before then). When I took Mid Tompkins's long range class he told us there was no point in having sight adjustments smaller than 1/2 moa for 1000 yard shooting. He said 1/4 moa wind changes usually happen faster than you can pause to turn the knob. If you see your neighboring competitor's spotter come up about a quarter moa to one side of where's he's been grouping, you do best not to waste time clicking sights, but rather to hold ever so barely detectably to the opposite side and get the round out of the tube before the wind changes its mind.

That tells you that most competitive Palma guns can shoot around 1/4 moa. He gets to that by soft seating, so a bullet contacts the lands, but is in a neck mouth with little enough friction that closing the bolt can finish the seating.
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